1. Field of the Invention
The present invention relates to a noise suppression structure for preventing noise such as friction sound and reverberation caused when sound from a speaker vibrates a speaker grille.
2. Background Art
For placing a speaker of a vehicle audio system in an interior of a vehicle (e.g. a car), a recess 2a for fitting a speaker grille 4 is formed in a position corresponding to a speaker opening 2 in an interior trim 1 (the position where the speaker grille 4 is attached), as shown in FIG. 4. The speaker opening 2 is opened in the recess 2a, and a speaker 3 is disposed in the speaker opening 2. The speaker grille 4 is fitted in the recess 2a so as to cover the speaker opening 2.
The speaker grille 4 is provided to protect the speaker 3 from an external shock and improve the appearance. The sound from the speaker 3 passes through sound holes 5 which are formed in a ceiling board 4a of the speaker grille 4. A flange 4b is formed in the periphery of the ceiling board 4a of the speaker grille 4. The speaker grille 4 can be detachably attached to the interior trim 1 by engaging hooks 8 provided at the end of the flange 4b with engaging holes la opened in the interior trim 1. A cylindrical-shaped sound guiding tube 6 for carrying sound from the speaker 3 to the sound holes 5 efficiently is extended downward from the ceiling board 4a of the speaker grille 4. The speaker grille 4 is detachably attached to the interior trim 1 for maintenance of the speaker 3.
The sound from the speaker 3 passes through the sound guiding tube 6 and the sound holes 5 of the speaker grille 4 and reaches the ears of a passenger.
The sound from the speaker 3 also vibrates the speaker grille 4. In the structure where the speaker grille 4 is detachably attached to the interior trim 1, when the speaker grille 4 vibrates, friction sound may be generated at contact parts between the speaker grille 4 and the interior trim 1 (specifically, each of retaining pars K1 between the engaging holes 1a and the hooks, contact part between an outer face K2 of the flange 4b and the interior trim 1 and contact part between a lower edge K3 of the flange 4b and the interior trim 1). And the friction sound is a noise offensive to the ear.
To address the problem, conventionally, non-woven fabric 7 is adhered to the contact parts of the speaker grille 4, the retaining part K1, the outer face K2 of the flange 4b, and the lower edge K3. Generally, adhesive material is provided on the back side of the non-woven fabric 7. With the adhesive material, the non-woven fabric 7 is adhered to the speaker grille 4).
As described above, adhesion of the non-woven fabric 7 to the parts K1 to K3 contacting with the interior trim 1 of the speaker grille 4, friction sound is generated between the speaker grille 4 and the interior trim 1.
However, adhesion of the non-woven fabric 7 piece by piece to the contact parts K1 to K3 is too complicated to be automated easily. Consequently, the non-woven fabric 7 is conventionally manually adhered. Such the manual work is very time consuming and inefficient which results in a variability in quality by workers.
In addition, there is the case that the adhesive material provided on the back side of the non-woven fabric 7 contains a hazardous material such as VOC (Volatile Organic Compound). When the hazardous material diffuses in a small vehicle compartment, it may be harmful to the health of a passenger.
Further, even when the generation of the friction sound is suppressed with adhering the non-woven fabric 7, a new problem arises such that another type of noise which had been hidden by the friction sound. Specifically, when the speaker grille 4 vibrates, the vibration sound generated at this time reverberates in a space X formed between the flange 4b and the sound guiding tube 6 of the speaker grille 4, and the reverberation becomes the new problem.